20 research outputs found
The influence of plant growth habit on calcium nutrition of groundnut (Arachis hypogaea L.) pods
In field experiments in India and Niger runner and bunch groundnut cultivars were compared for their pod distribution pattern and its relevance to the calcium (Ca) supply for pod development. Bunch cultivars produced sixty to eighty percent of their pods within 5 cm of the tap root. Runner cultivars explored a radius of up to 30 cm for pod production and exploited the soil area in a more homogeneous manner than bunch types. The available soil volume per pod was 19 to 27 cm3 for bunch types and 43 to 46 cm3 for runner types, varying the potential for Ca competition between pods. Computation of the soil Ca content needed to satisfy pod Ca requirements showed that much higher concentrations were needed for the bunch cultivars than for the runners. No significant differences in Ca content of pods existed between bunch and runner cultivars. However, in the runner cultivars, the Ca content of the more widely dispersed pods in outer zones was greater than that of the more densely populated inner pod zones. Regression analysis of shelling percentage across a range of environments showed that the shelling percentage of runners declined less rapidly than did the shelling percent of bunch types, indicating that runners were more efficient in exploiting Ca at lower soil Ca availability than the bunch type
Sources of Variation in Shelling Percentage in Peanut Germplasm and Crop Improvement for Calcium Deficiency-Prone Soils
Calcium (Ca) deficiency causes peanut pegs and pods to abort, resulting in decreased shelling percentages and yields. Environmental factors influencing calcium availability include soil Ca content and soil moisture. Genetic attributes that influence the sensitivity of cultivars to soil Ca supply include pod size, soil volume per pod (varied by plant growth habit), and pod wall attributes. Where Ca fertilization is not possible, genetic solutions to Ca deficiency are important, and breeders need information on the relative importance of these attributes. The objective of this research was to quantify the relative importance of these three sources of variation. Data from three trials were used to evaluate the relative importance of these attributes. The trials, sited on Ca-deficient alfisols, used between four and 12 germplasm lines with varied Ca sensitivity- determining attributes. Lines differed in growth habit (spreading or bunch), pod volume, pod yield, shelling percentage, and seed yield. The trial treatments and environments (sites and seasons) also varied Ca supply through soil type, fertilization, and water supply. Assuming that Ca supply has little impact on crop growth rates (CGR), a physiological model was used to set aside the contributions of CGR to yield differences between treatments. The three trials were analyzed separately and then combined for further regression analysis by defining each site and treatment combination as an environment. Within trials, variations in shelling percentage accounted for up to half the variations in seed yield between lines. In the combined analysis, easily selected attributes—pod volume (58% of germplasm sums of squares) and plant habit (8%) and their interaction (14%)—accounted for much of the variation in shelling percentage. The interaction was due to shelling percentage being less influenced by pod volume in spreading than in the bunch types. Thus, in Ca-limiting situations, the spreading growth habit allowed larger seeded peanuts to be grown than the bunch growth habit because of the greater pod dispersal of this type. Assuming that the lines tested typified peanuts for their relation between attributes and Ca deficiency-based shelling percentage variations, breeders should place the greatest emphasis on small pod size to decrease peanut sensitivity to Ca deficiency. Increased soil available to each pod by pod dispersal decreases the need for small pods to decrease sensitivity to Ca-deficient soil
The influence of plant growth habit on calcium nutrition of groundnut (Arachis hypogaea L.) pods
Effect of Jasmonate and Salicylic Acid Treatments on Fruit Maturation in Japanese Persimmon
Influence of temperature and soil drying on respiration of individual roots in citrus: integrating greenhouse observations into a predictive model for the field
In citrus, the majority of fine roots are distributed near the soil surface - a region where conditions are frequently dry and temperatures fluctuate considerably. To develop a better understanding of the relationship between changes in soil conditions and a plant's below-ground respiratory costs, the effects of temperature and soil drying on citrus root respiration were quantified in controlled greenhouse experiments. Chambers designed for measuring the respiration of individual roots were used. Under moist soil conditions, root respiration in citrus increased exponentially with changes in soil temperature (Q(10) = 1.8-2.0), provided that the changes in temperature were short-term. However, when temperatures were held constant, root respiration did not increase exponentially with increasing temperatures. Instead, the roots acclimated to controlled temperatures above 23 degreesC, thereby reducing their metabolism in warmer soils. Under drying soil conditions, root respiration decreased gradually beginning at 6% soil water content and reached a minimum at <2% soil water content in sandy soil. A model was constructed from greenhouse data to predict diurnal patterns of fine root respiration based on temperature and soil water content. The model was then validated in the field using data obtained by CO2 trapping on root systems of mature citrus trees. The trees were grown at a site where the soil temperature and water content were manipulated. Respiration predicted by the model was in general agreement with observed rates, which indicates the model may be used to estimate entire root system respiration for citrus. [KEYWORDS: root distribution, simulation, soil water content, temperature]
Estimating age-dependent costs and benefits of roots with contrasting life span: comparing apples and oranges
The relation between root age and root function is poorly understood, despite its importance to root longevity. The effect of root age on respiration rates and P-32-uptake kinetics was determined for roots excavated from mature apple and citrus trees (median root life spans of 30 vs 300 d). To evaluate whether root longevity maximizes the efficiency of nutrient capture, daily and lifetime efficiencies were calculated by dividing simulated P-uptake benefits (solute transport model) by age-specific respiration costs. We found that respiration rates and P uptake capacity change with root age in a species-specific way; and soil characteristics that determine the rate of nutrient depletion in the rhizosphere are as important as changes in root physiology in determining the age at which a root reaches its maximum efficiency. Further testing of the efficiency of nutrient capture as a predictor of root life span requires measurement of both soil properties and age-specific physiology of roots including their mycorrhizal fungi. [KEYWORDS: apple; citrus; minirhizotron; P-32; respiration; phosphorus uptake; root life span; root turnover; root age; simulation modelling; uptake kinetics Daily patterns; water status; fine roots; respiration; dynamics; field; turnover; carbon; growth; model]